In its written response to the Office of Fair Trading's draft decision to refer the sector to the Competition Commission, the ACS said that it was concerned that the decision may exclude key products such as fuel and non-food.
It added that it has shown the way in which supermarket price fuel damages competition for local fuel customers and has a strong link to grocery shopping.
ACS chief executive, David Rae said: "It is vitally important that the Competition Commission investigates how supermarket's price fuel, which is a clear example of where supermarket's deliver different prices to different consumers based entirely on location and local competition, and it is severely damaging the independent forecourt convenience store market.”
He added: "We welcome the OFT's decision to allow a full investigation of the grocery market. This inquiry presents a once in a lifetime opportunity to address the worrying trends in the grocery market.
“We will argue strongly for action that will ensure consumers get the best, most competitive grocery market, that has real choice and diversity for the long term.”